Ethnologue and ISO list an Iranian language "Khalaj" with the same population,[4] but Glottolog states it does not exist.[5] The Khalaj speak their Turkic language and Farsi, and the supposed Iranian language of the Khalaj is spurious.[6]

Further, features such as preservation of three vowel lengths, preservation of word-initial Proto-Turkic *h, and lack of the sound change *d → y has led to a non-Oghuz classification of Khalaj. An example of these archaisms is present in the word hadaq ("foot"), which has preserved the initial *h and medial *d. The equivalent form in nearby Oghuz dialects is ayaq (compare Turkishayak). Therefore, it is an independent language that became distinct very early from other extant Turkic languages.[7][8] Because of the preservation of these archaic features, some scholars have speculated that the Khalaj are the descendants of the Arghu Turks. It's considered as "last examples" of Old Turkic by some Turkish scholars.[9]

Khalaj is spoken mainly in Markazi Province in Iran. Doerfer cites the number of speakers as approximately 17,000 in 1968; the Ethnologue reports that the population of speakers grew to 42,107 by 2000.

It is often claimed that vowels in Khalaj occur in three lengths: long (e.g. [qaːn] 'blood'), half-long (e.g. [baˑʃ] 'head'), and short (e.g. [hat] 'horse'). This view has been challenged by A. Manaster Ramer.[10] Additionally, some vowels are realized as falling diphthongs, as in [quo̯l] ('arm, sleeve').